An accurate measurement of the black hole spin in GX 339-4

Rubens Reis, institute of astronomy

We present the most accurate measurement to date of the dimensionless spin parameter of a black hole. The spin parameter of the Galactic black hole binary GX 339-4 is estimated by modeling the strong reflection signatures present in the XMM-Newton observations of GX 339-4 in both its very high and low hard states. Using a newly developed, self-consistent reflection model which implicitly includes the blackbody radiation of the disc as well as the effect of Comptonisation, blurred with a relativistic line function, we infer the spin parameter of GX 339-4 to be 0.935 +\- 0.01 (statistical) +\- 0.01 (systematic) at 90 per cent confidence. Our technique is independent of the black hole mass and distance, the uncertainties of which are the main contributors to the spin uncertainty in previous works.